A quantitative evaluation of damage in normal appearing white matter in patients with multiple sclerosis using diffusion tensor MR imaging at 3 T

Correlation between functional MRI techniques and early disability in ambulatory patients with relapsing–remitting MS

Background

Multiple sclerosis (MS) is a common neurological disorder which can lead to an occasional damage to the central nervous system. Conventional magnetic resonance imaging (cMRI) is an important modality in the diagnosis of MS; however, correlation between cMRI findings and clinical impairment is weak. Non-conventional MRI techniques including apparent diffusion coefficient (ADC) and magnetic resonance spectroscopy (MRS) investigate the metabolic changes over the course of MS and overcome the limits of cMRI.

A total of 80 patients with MS and 20 age and sex-matched healthy control subjects were enrolled in this cross-sectional study. Ambulatory patients with relapsing–remitting MS (RRMS) were recruited. Expanded Disability Status Scale (EDSS) was used to assess the disability and the patients were categorized into three groups “no disability”, “minimal disability” and “moderate disability”. All patients underwent cMRI techniques. ADC was measured in MS plaques and in normal appearing white matter (NAWM) adjacent and around the plaque. All metabolites concentrations were expressed as ratios including N-acetyl-aspartate/creatine (NAA/Cr), choline/N-acetyl-aspartate (Cho/NAA) and choline/creatine (Cho/Cr). ADC and metabolite concentrations were measured in the normal white matter of 20 healthy control subjects.

Results

The study was carried on 80 MS patients [36 males (45%) and 44 females (55%)] and 20 healthy control [8 males (40%) and 12 females (60%)]. The ADC values and MRS parameters in NAWM of patients with MS were significantly different from those of the control group. The number of the plaques on T2 images and black holes were significantly higher at “Minimal disability” group. Most of the enhanced plaques were at the “Moderate disability” group with P value < 0.001. The mean of ADC in the group 1, 2 and 3 of disability was 1.12 ± 0.19, 1.50 ± 0.35, 1.51 ± 0.36, respectively, with P value < 0. 001. In the group 1, 2 and 3 of disability, the mean of NAA/Cr ratio at the plaque was 1.34 ± 0.44, 1.59 ± 0.51 and 1.11 ± 0.15, respectively, with P value equal 0.001.

Conclusion

The non-conventional quantitative MRI techniques are useful tools for detection of early disability in MS patients.

The Relevance of Neuroimaging Findings to Physical Disability in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system and one of the leading causes of disability in young adults. While some patients with MS have a benign course in which they develop limited disability even after many years, other patients have a rapidly progressive course resulting in severe disability. However, the progression of the disease, particularly disability, is currently a predictable course with neuroimaging features to some extend. Magnetic resonance imaging (MRI) is not only the main diagnostic tool but also used to monitor response to therapies, thanks to its high sensitivity and ability to identify clinically silent lesions. This report presents a literature review which examines in detail the relationship between MRI findings and disability.

Restriction spectrum imaging of white matter and its relation to neurological disability in multiple sclerosis

BACKGROUND

Restriction spectrum imaging (RSI) is a recently introduced magnetic resonance imaging diffusion technique. The utility of RSI in multiple sclerosis (MS) is unknown.

OBJECTIVE

To investigate the association between RSI-derived parameters and neurological disability in MS.

METHODS

Seventy-seven relapsing-remitting MS patients were scanned with RSI on a 3-T scanner. RSI-derived parameters: fast and slow apparent diffusion coefficient (sADC), fractional anisotropy, restricted fractional anisotropy, neurite density (ND), cellularity, extracellular water fraction, and free water fraction, were obtained in white matter lesions (WML) and normal appearing white matter (NAWM). Patients were divided into three groups according to their expanded disability status scale (EDSS): with minimal, low, and substantial disability (<2.5, 2.5-3, and >3, respectively). Group comparisons and correlation analyses were performed.

RESULTS

All tested RSI-derived parameters differed between WML and NAWM ( p < 0.001 for all pairwise comparisons). The sADC in WML showed largest difference across disability subgroups (analysis of variance (ANOVA): F = 5.1, η² = 0.12, p = 0.008). ND in NAWM showed strongest correlation with disability (ϱ = -0.39, p < 0.001).

CONCLUSION

The strongest correlation with EDSS of ND obtained in NAWM indicates that processes outside lesions are important for disability in MS. Our study suggests that RSI-derived parameters may help understand the "clinico-radiological paradox" and improve disease monitoring in MS.

Fibre-specific white matter changes in multiple sclerosis patients with optic neuritis

Long term irreversible disability in multiple sclerosis (MS) is thought to be primarily driven by axonal degeneration. Axonal degeneration leads to degenerative atrophy, therefore early markers of axonal degeneration are required to predict clinical disability and treatment efficacy. Given that additional pathologies such as inflammation, demyelination and oedema are also present in MS, it is essential to develop axonal markers that are not confounded by these processes. The present study investigated a novel method for measuring axonal degeneration in MS based on high angular resolution diffusion magnetic resonance imaging. Unlike standard methods, this novel method involved advanced acquisition and modelling for improved axonal sensitivity and specificity. Recent work has developed analytical methods, two novel axonal markers, fibre density and cross-section, that can be estimated for each fibre direction in each voxel (termed a “fixel”). This technique, termed fixel-based analysis, thus simultaneously estimates axonal density and white matter atrophy from specific white matter tracts. Diffusion-weighted imaging datasets were acquired for 17 patients with a history of acute unilateral optic neuritis (35.3 ± 10.2 years, 11 females) and 14 healthy controls (32.7 ± 4.8 years, 8 females) on a 3 T scanner. Fibre density values were compared to standard diffusion tensor imaging parameters (fractional anisotropy and mean diffusivity) in lesions and normal appearing white matter. Group comparisons were performed for each fixel to assess putative differences in fibre density and fibre cross-section. Fibre density was observed to have a comparable sensitivity to fractional anisotropy for detecting white matter pathology in MS, but was not affected by crossing axonal fibres. Whole brain fixel-based analysis revealed significant reductions in fibre density and fibre cross-section in the inferior fronto-occipital fasciculus (including the optic radiations) of patients compared to controls. We interpret this result to indicate that this fixel-based approach is able to detect early loss of fibre density and cross-section in the optic radiations in MS patients with a history of optic neuritis. Fibre-specific markers of axonal degeneration should be investigated further for use in early stage therapeutic trials, or to monitor axonal injury in early stage MS.

•

Fibre density is reduced in lesions and normal-appearing white matter in MS

•

Fibre density detects white matter pathology in regions of crossing fibres

•

Loss of fibre density and cross-section selectively evident in visual pathways of optic neuritis patients.

Test-Retest and Interreader Reproducibility of Semiautomated Atlas-Based Analysis of Diffusion Tensor Imaging Data in Acute Cervical Spine Trauma in Adult Patients

BACKGROUND AND PURPOSE

DTI is a tool for microstructural spinal cord injury evaluation. This study evaluated the reproducibility of a semiautomated segmentation algorithm of spinal cord DTI.

MATERIALS AND METHODS

Forty-two consecutive patients undergoing acute trauma cervical spine MR imaging underwent 2 axial DTI scans in addition to their clinical scan. The datasets were put through a semiautomated probabilistic segmentation algorithm that selected white matter, gray matter, and 24 individual white matter tracts. Regional and white matter tract volume, fractional anisotropy, and mean diffusivity values were calculated. Two readers performed the nonautomated steps to evaluate interreader reproducibility. The coefficient of variation and intraclass correlation coefficient were used to assess test-retest and interreader reproducibility.

RESULTS

Of 42 patients, 30 had useable data. Test-retest reproducibility of fractional anisotropy was high for white matter as a whole (coefficient of variation, 3.8%; intraclass correlation coefficient, 0.93). Test-retest coefficient-of-variation ranged from 8.0%-18.2% and intraclass correlation coefficients from 0.47-0.80 across individual white matter tracts. Mean diffusivity metrics also had high test-retest reproducibility (white matter: coefficient-of-variation, 5.6%; intraclass correlation coefficient, 0.86) with coefficients of variation from 11.6%-18.3% and intraclass correlation coefficients from 0.57-0.74 across individual tracts, with better agreement for larger tracts. The coefficients of variation of fractional anisotropy and mean diffusivity both had significant negative relationships with white matter volume (26%-27% decrease for each doubling of white matter volume, P < .01).

CONCLUSIONS

DTI spinal cord segmentation is reproducible in the setting of acute spine trauma, specifically for larger white matter tracts and total white or gray matter.

Quantifying the Susceptibility Variation of Normal-Appearing White Matter in Multiple Sclerosis by Quantitative Susceptibility Mapping

OBJECTIVE

The purpose of this study is to evaluate the magnetic susceptibility of normal-appearing white matter (NAWM) in patients with multiple sclerosis (MS) using quantitative susceptibility mapping.

MATERIALS AND METHODS

Ninety-four patients with relapse-remitting MS (RRMS) (37 with gadolinium-enhancing lesions and 57 with only gadolinium-nonenhancing lesions) and 55 healthy control subjects were included in this retrospective study. The susceptibility values of NAWM relative to CSF in patients with MS were compared with those of white matter (WM) in healthy control subjects and were correlated with the patient status of gadolinium-enhancing lesions, disease duration, and expanded disability status scale scores.

RESULTS

All 37 patients with RRMS and gadolinium-enhancing lesions also had gadolinium-nonenhancing lesions. Susceptibility values of NAWM in patients with MS and only gadolinium-nonenhancing lesions (-18.29 ± 8.03 parts per billion [ppb]) were higher than those for WM in healthy control subjects (-25.81 ± 6.02 ppb; p < 0.001) and NAWM in patients with gadolinium-enhancing lesions (-25.64 ± 6.55 ppb; p < 0.001). Susceptibility values of NAWM in patients with MS with gadolinium-enhancing lesions were similar to those for WM in healthy control subjects (p = 0.91). This trend was dependent on neither NAWM region nor disease duration when the data were controlled for age. NAWM susceptibility was not correlated with either disease duration or expanded disability status scale (p > 0.05).

CONCLUSION

In patients with RRMS and gadolinium-nonenhancing lesions, the susceptibility values of NAWM decrease when gadolinium-enhancing lesions appear, approaching values similar to those of WM in healthy control subjects, suggesting that NAWM may contribute to the iron accumulation observed in early active MS lesions.

Diffusion tensor imaging of occult injury of optic radiation following optic neuritis in multiple sclerosis

Multiple sclerosis (MS) is easily detected by routine magnetic resonance imaging (MRI). However, it is not possible to detect early or occult lesions in MS by routine MRI, and this may explain the inconsistency between the severity of the lesions found by MRI and the degree of clinical disability of patients with MS. The present study included 10 patients with relapsing-remitting MS and 10 healthy volunteers. Each patient underwent routine 3.0 T MRI, diffusion tensor imaging (DTI), and diffusion tensor tractography (DTT). Optic nerve and optic radiation were analyzed by DTI and DTT. The fractional anisotropy (FA), mean diffusivity (MD), λ_//, and λ_┴ values were measured. In the 10 patients with MS, 7 optic nerves were affected, and 13 optic nerves were not affected. Cranial MRI showed that optic nerve thickening and hyperintensity occurred in 2 patients with MS. In the directionally encoded color maps, a hypointensive green signal in the optic nerve was observed in 3 patients with MS. The FA values were significantly lower and the MD, λ_//, and λ_┴ values were significantly higher in the affected and unaffected optic nerves and optic radiations in patients with MS in comparison with controls (P<0.05). There were no significant differences in these values between the affected and unaffected optic nerves and optic radiation in patients with MS (P>0.05). Diffusion tensor imaging is sensitive in the detection of occult injury of the optic nerve and optic radiation following optic neuritis. Diffusion tensor imaging may be a useful tool for the early diagnosis, treatment and management of MS.